Web tension control means



Dec. 19, 1961 Filed Sept. 15, 1958 E. D. BEACHLER WEB TENSION CONTROL MEANS 3 Sheets-Shea?l l Fall Pos1 lolz Liz/EEDT Dec. 19, 1961 E- D- BEACHLER 3,013,707

WEB TENSION CONTROL MEANS Filed Sept. l5, 1958 v5 Sheets-Sheet 2 T mzfa ILDT ELI/warb Bead/1 lez",

Dec. 19, 1961 E. D. BEACHLER 3,013,707

I WEB TENSION CONTROL MEANS Filed Sept. l5, 1958 5 Sheets-Sheet 5 E U21/ard' D Bead/5 /er United States Patent() 3,013,707 WEB TENSIONl CUNTROL MEANS Edward D. Beachler, Beloit, Wis., assigner to Beloit Iron Works, Beloit, Wis., a corporation of Wisconsin Filed Sept. 15, 1958, Ser. No. 760,918 4 Claims. (Cl. 22a-408) This invention relates to improvements in apparatus, for guiding and carrying a travelling length of web material such as paper and more particularly to` a device having mechanism capable of maintaining constant control of a web span by applying a take-up force to accommodate substantial change in length of the web span.

The present invention contemplates embodiment in a machine having a traveling web, such as a paper machine, wherein a web of paper is carried through a machine on rolls along a processing path, and processing apparatus is located along the path to treat the paper web. In paper making and paper converting, it is essential that the web be kept under complete control at all times in order to avoid sag of the sheet or flutter which would permit it to wrinkle or crease or to leave its proper path of travel in any way.

Control of the web will be lost with sudden reduction in tension in the web such as caused by rapid reduction in ltensile strength, for example, such as occurs with moisture increase. Reduction in tension can occur at times when the driving forces along the web are reduced, such as during starting periods.

Paper, like most material, will have a unit length corresponding to the unit lo-ad or stress. Therefore, an enforced change in length will result in a change in stress. Also, a change in stress will result in a change of length. In a moving web this change in length is accounted for and compensated by the speed ratio of difference in surface speed of the carrying rolls when the web is supported on rotating rolls. Thus, if a web span is under tension which results in' an increase in length the roll or rolls receiving the span must have a greater surface speed than those delivering the span.

Changes in strength may be due to a change in moisture content of the web or may be due to a change of grade of material or its Weight or thickness. Even ambient humidity may have an effect on the span length. Furthermore, a change in treatment upstream from the span may likewise affect the tension and therefore span length. In paper machines, this might, for example be caused by a change in the extrusion effect by the prior process such as is due to a change in press or calender nip loading. Diiiiculties may also occur during webhing up or some period when the operation is unstable, as for example when an increase in or a fresh application of coating material is applied to the web. When the machine is star-ted or when afresh web is threaded into the machine or when the width of the web tail varies such as widening to a full sheet the problem of span variation is encountered.

The present invention contemplates providing a takeup or control mechanism which holds a take-up roll against the surface of a web of material between the rolls supporting a span of material. A considerable variation in the position of the take-up roll may be necessary with change in strength of the web.

Among the problems encountered in the provision of a take-up roll which has a long path of travel to accommodate large variations in span length, are the variations in the tensioning effect on the web material with changes in the angle of Wrap or amount of web wrap around the take-up roll. Other problems encountered include the changes in effect of the roll weight on a roll support when the roll changes its position due to change in length of web span.

An object of the invention is to provide a roll positioning device which holds the roll against the web span with a varying force which is a function of roll position and which automatically compensates for the varying force factors caused by change in roll position.

An object of the invention is to provide a mechanism for applying a take-up force to a web span which will have a long travel to accommodate changes in strength of the web and follow the span and t-ake up stretch in the span to keep the sudden change of length of span under control. Another object is also to provide such a long travel take-up mechanism to take up slack in the web span when the tensioning forces applied by the carrying rolls are reduced such as during starting or webhing up periods.

Another object of the invention is to provi-de an improved novel and useful means of taking up the slack in a travelling web either at constant tension or at a predetermined rate of change in tension which may be an increasing or decreasing function of the span length.

An object of the invention is to provide a mechanism which will apply a tensioning force to a span of a moving paper web wherein the apparatus will accommodate substantial changes in length of the span, such as result from variations in strength of the paper or variations in the speed of rolls carrying the paper.

Another object of the invention is -to provide an improved take-up roll assembly for applying a tensioning force to a span of la moving paper web which has a long trafvel toaccommodate changes in span length and yet maintains a predetermined uniform web tension and maintains control of the web.

A feature of the invention is the provision of a movably mounted take-up roll to engage a span of moving paper web or the like and apply a tensioning force to the loop formed in the span with a roll guiding means supporting the roll over a long 4take-up path. A variable rate air spring applies a tensioning force to the roll to maintain a predetermined tension in the web span, automatically compensating for factors such as the force of the weight of the roll on the support mechanism which varies with the change of the position of the roll, and the force of the web tension on the roll which varies with roll position.

Other objects and features of the present invention will become more apparent with the teachings of the principles of the invention, and the disclosure of the preferred embodiment in the specification, claims and drawings, in which:

FIGURE l is a fron-t elevational view of a paper mai chine embodying mechanism utilizing the principles of the present invention;

FIGURE 2 is a detailed elevational view of a take-up and tensioning roll assembly; y

FIGURE 3 is a side elevational view of the roll assembly of FIGURE 2; and

FIGURES 4 and 5 are graphs illustrating the relationship of forces pertaining to 4tensioning a web span.

As shown on the drawings.'

As illustrated particularly in FIGURE 1, a section o a paper machine is illustrated with a continuous lweb of paper 6 being drawn through the machine along a processing path `and supported by rolls. Along the processing path is located processing equipment for treating the paper web. The web 6 is illustrated as moving downwardly through a calendar stack of rolls 8 with a lower supporting roll l0 at the base of the calendar stack.l `T he web 6 leaves the supporting roll 10 to next thread over a supporting roll 12 to define a span 6a of the paper web therebetween. This span may be referred to as the tensioning span with a take-up roll i4 engaging and applying Patented Dec. 1,9, 1961 a take up force to the span or loop 6a between the support rolls 10 and 12 defining the span to hold the web taut and prevent free flutter and consequent damage to the web.

The web next enters a group of rolls which form processing apparatus 16 for the web. The web first passes over a guide roll 18 and moves into the nip formed between the upper and lower coater drums 2t) and Z2, respectively. Coating material may he supplied to the drum 20 from a supply roll 21 dipping into a coating pan 24. Coating material may be supplied to the drum 22 by a coating distributing roll 26 dipping into a coating pan 2S. The coating drums are driven and aid in drawing the web 6 forwardly through the machine.

With the take-up roll applying a force to attain a predetermined tension in the web, the roll will move against the web until the tension is attained. The length of the tensioning loop or span 6:1 will then vary as the strength of the paper web 6 varies and will also vary as the tension forces applied by the rolls carrying the span vary. The strength may be affected by the inherent action of mechanism such as the coating rolls which effect a sudden change in the moisture content of the paper web or such as by changes in ambient humidity. The strength will also vary with the width of the paper web such as occurs when a fresh web is threaded into the machine and the strip widens to the full web width. The forces applied by the rolls vary in accordance with the difference in speed between the roll drawing the lead end of the span and the roll at the trailing end of the span. During the o start-up periods variation in forces occur As the machine picks up speed, the tension will generally increase, and the span 6a will become shorter.

A feature of the present invention is the provision of a control assembly for the take-up roll 14 which will maintain a tension control on the roll preventing tiutter and preventing the formation of a free loop or span with sudden changes in the length of the take-up loop or span 6a and with large changes in span length.

A take-up roll assembly is shown in detail in FIGURES 2 and 3, with the span rolls 10 and 12 shown diagram matically and, therefore, in a slightly different position than that illustrated in FIGURE 1. In FIGURE 2, the variations in stretch of the take-up loop 6a are illustrated as ranging from the position of the taire-up tensioning roll 14' when the loop stretches to its maximum dovm position to the position 14" where the loop span is at its shortest position.

The take-up roll 14 is illustrated in FIGURES 2 and 3 as supported on pivotal arms 3% and 32 which are secured to a pivotal support shaft 34. The pivotal arms support bearings 36 and 33 at their ends in which a take-up roil shaft 4t) is rotatably supported. rI`he pivotal shaft 34 is supported in bearings 42 and 44 mounted on frame columns 46 and 48.

While the take-up roll 14 may be free rotating, it is shown as being driven at the speed of the moving web by a motor 47 having a drive pulley 49 which drives a belt 50 threaded over a pulley 52 on the shaft 40 of the tension roll 14. A belt tensioning pulley S4 controls the tension of the belt 50. The motor is mounted so that its shaft is coaxial with the pivotal shaft 34 to permit pivotal movement of the arms and 32 without changing the length between the centers of the pulleys 49 and 52.

The pivotal position of the support shaft 34, and hence the position of the take-up roll 14, may be measured by indicator mechanism including a bracket 35 secured to the end of the shaft 34, and having arms projecting radially from the axis of the shaft. To one of the arms 37 is connected a line 39, and to the other arm 41 is connected another line 43. The lines pass over a double guide sheave 45 and extend upwardly over sheaves 47a and 49a to connect to an indicator mechanism which will in turn show the position of the take-up roll 14.

The web take-up force on the take-up roll 14 is Controlled by a resilient spring which is in the form of an air spring with air springs provided at and 62. The air spring may be constructed to have a characteristic which will vary the tension in the web as a function of span length, or in other words as a function of roll position as shown, for example by the broken line curve 59 in FIG- URE 5. However, for purposes of description the mechanism will be generally referred to as maintaining a constant tension in the web, as shown by the straight line curve There are two variables to be contended with in determining the force characteristic of the air spring. It may be observed in FIGURE 2, as the span length changes from the position of the take-up roll from 14 to 14 the angie of wrap of the web around the roll changes. Thus, the effect of a unit of force of the roll against the web also changes and it will be observed that in the position of the take-up roll of 14", the force of the take-up roll will have a much greater tensioning effect than the force of the take-up roll in the position 14.

The other variable is the force of the weight of the roll on the takeup support shaft 34. When the take-up roll is in the position 14 its weight will not create as much torque on the take-up shaft as it will when the roll is in the position 14".

To compensate for these variables with variance in roll position, the characteristics of the take-up spring is dcsigned to accommodate the variables. As illustrated in FIGURE 4, the torque on the take-up shaft 34 is plotted against roll position. Curve 61 shows the effect of the weight of the roll as the roll moves from a position above the shaft to a position horizontally opposite the shaft. The curve 63 shows the reaction force of the web for any given tension in the web for variances in roll position.

To obtain the desired characteristics of the take-up spring, the curves 61 and 63 are added and the resultant curve is the characteristic desired for the take-up spring. The web reaction force is plotted as a positive force in the graph of FIGURE 4 and the weight of the roll is plotted as a negative force with the force of the take-up spring being a positive force to counter-balance the weight of the roll. It will be understood that in certain circumstances the spring may be arranged to apply a torque in the opposite direction. such as where the weight of the roll does not have suliicient force to achieve the desired tension in the web and this weight must be augmented by a spring force.

With the characteristic of the take-up spring determined, variances in tension may be obtained by changing the air pressure within the spring. With a spring designed to obtain constant web tension the tension will be constant regardless of roll position as shown by the curve 65 in FIGURE 5.

As previously mentioned, in certain circumstances it may be desirable to obtain a web tension which varies as ya function of roll position and this variance will then be obtained by providing a take-up spring having a characteristic to obtain the desired roll force for web tension with respect to roll position. Still taking into consideration the variable factors shown in FIGURE 4 such a spring could be constructed, for example, by plotting the curve 63 and using the values of desired variable web tension relative to roll positions instead of the constant web tension as was used with the curve shown at 63.

In the embodiment illustrated, the air spring means does not apply ia direct tensioning force to the tensioning roll 14, but instead applies a net -force by assuming a portion of the weight of the tensioning roll with the remainder being the tensioning force applied to the web.

For this purpose, the arms 30 and 32 are in the general shape of a bell crank with lower extension arms 56 and 58, respectively, connected to air springs 60 and 62. The spring 60 is mounted on a bracket 64 secured to a frame piece 66 at the top of the column 46 and the air spring 62 is mounted on a bracket 68 secured to a frame piece 70 on the top of the column 48. The air springs are substantially identical in construction and, therefore, only the spring 6i? need be described in detail.

The air spring 60 is provided with an expandable bellows 60a having annular support wires 6019 and 60C with the bellows lattached to end plates 60d and 60e. The end plate 60e is mounted on the bracket 64. The end plate 60a' is provided with a bifurcated connector 60] receiving a pivotal pin 72 to connect the lower arm 56 of the arm 30. The spring thus applies a supporting tensioning force to the roll 14. An adjustable stop bolt 74 is threaded into the frame piece 66 to limit the expansion of the bellows 60.

The lower limit of movement of the roll 14 is determined by radial stop arms 76 and 7S secured to the pivotal shaft 34, and engaging stop bosses S0 and 82 which project from the frame piece 66 and 70, and which have threaded openings 34 and 86 for an adjustable stop screw, not shown.

The air spring 60 may be provided with iniiating means, not shown, which will change the force of the spring. Thus, with predetermined fixed amounts of yair pressure within the spring, a predetermined tension can be obtained in the web.

In operation, the web 6 is drawn through the machine at a relatively high rate of speed, and the take-up roll 14 applies a lateral pressure to the span 6a to tension the paper web. With variations in web strength, such as caused by changing in moisture of the web, the take-up roll will move between the positions 14 and 14, as shown in FiGURE 2 to maintain the web under control and to main-tain a tension therein. rl`he air spring 69 has a load deflection characteristic wherein a proportionate amount of the weight of the tensioning roll 14 and its arms 30 and 32 is supported so that the net weight of the roll will apply a tensioning force to maintain a constant tension in the web.

Thus, the web will be continually under control du.- ing periods of variation in `speed and with variation in strength of the paper web.

Thus, it will be seen that I have provided an improved paper machine employing -a take-up roll assembly which meets the objectives and advantages hereinbefore set forth. The mechanism is well adapted to accommodat- `ing webs of any length, since the weight of the roll is fully compensated for and is not a factor which will adversely atiect operation. Further the variance in force due to change in the angle of wrap of the web around the roll with change in roll position is fully compensated for. The possibility of absolute control of the load deection characteristic of the `air spring atiords the construction wherein the tension produced in the web with respect to the position of the roll can be varied at will.

l have, `in the drawings and speciiication, presented a detailed disclosure of the preferred embodiment of my invention, and it is to be understood that I do not intend to limit the invention to the speciiic form disclosed, but intend to cover all modifications, changes and alternative constructions and methods falling within the scope of the principles taught by my invention.

I claim -as my invention:

l. A mechanism for performing a continuing process on a rapidly traveling web of paper comprising means for supporting and :driving a web of paper along a processing path, spaced supporting means having a span length of paper web therebetween, a take-up roll located between said spaced supporting means for applying `a force to the web to compensate for variations in length of web between said supporting means, a guide for the roll guiding it over a relatively long range of movement between said `supporting means to accommodate variations in span length of the web, and a resilient closed chamber containing a compres'sible uid and having a iiexible wall and connected to apply a supporting force to the tape-up roll, said closed chamber having a force-length characteristie which applies said supporting force in proportion to the effective weight of the roll and in proportion to the ch-ange -in the component of force linearly along the web resulting from the change in angle of wrap to maintain a predetermined tension in the web regardless of roll position.

2, A machine 'for handling a traveling web comprising spaced support means for supporting a span of a continuously moving web, `a take-up roll positioned to engage said web span between said support means and to apply a force to the span to take up slack in the web with variations in web length in the span, and spring means including a resilient closed chamber containing a compressible iiuid and having a flexible Wall and being connected to apply a supporting force to said take-up roll, and having a force-length ch-aracteristic which applies said supporting force in proportion to the change in the component of force linearly along the web resulting from the change in angle of wrap and in proportion to the effective weight of the roll to maintain a predetermined tension in the web regardless of the position of the take-up roll.

3. A machine for-handling a traveling web comprising spaced support meansA for supporting a span of a continuously moving web, a take-up roll positioned to eugage said web span between said support means yand to apply a force to the span to take up slack in the web with variations in web length in the span, pivotally mounted arms supporting said take-up roll, and a resilient closed chamber containing a compressible fluid and having a flexible Wall and connected to apply a force to the arms, said closed chamber having a force-length characteristic which applies ysaid yforce in proportion to the change in the component of force linearly along the web resulting from the change in angle of wrap `and in proportion to the effective weight of the roll and arms to main-tain a predetermined tension in the web regardless of the position of the take-up roll.

4. A machine for handling a traveling web comprising spaced support means for supporting a span of a continuously moving web, a take-up roll positioned to engage said web span between said support means and to apply a force to the span to take up slack in the web with variations in web length in the span, pivotally mounted arms supporting said take-up roll, a resilient closed chamber containing a compressible fluid and having a flexible wall and connected to Iapply a force `to the arms, said closed chamber having a force-length characteristic which yapplies said force in proportion to the change in the component of force linearly along the web resulting from the change in angle of wrap and in proportion to the etfeotive weight of the roll Iand arms to maintain a predetermined tension in the web regardless of the position of the take up roll, Iand means for changingthe quantity of fluid in said chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,538,977 Feybusch et al. May 26, 1925 2,076,421 Wood Apr. .6, 1937 2,189,059 Dearsley Feb. 6, 1940 2,650,823 Chambon Sept. 1, 1953 2,766,717 Neidich et al. Oct. 16, 1956 2,774,327 Saint-Hilaire Dec. 18, 1956 2,877,010 Gouirand Mar. 10, 1959 

